Rivers around the world discharged approximately 263,000 tonnes of microplastics into the oceans in 2022, with 96 per cent of this originating from the Global South. This is the main finding of a study that has analysed various data sources showing that extreme rainfall events can substantially increase this transport of microplastics, particularly in regions with high plastic use and poor waste management. The authors, whose findings are published in Science, warn that climate change could exacerbate the problem as extreme rainfall becomes more frequent and intense.

Cities’ adaptation to climate change is not progressing fast enough to protect their inhabitants from increasing heatwaves, infectious diseases and exposure to pollen, which are having an ever-greater impact on the urban population. This is the main conclusion of a study published in The Lancet Public Health, based on 28 indicators from more than 850 European cities, including many in Spain such as Madrid, Barcelona and Valencia. The greatest improvements were observed in cities that increased their green space. The study also suggests that risks are rising more rapidly in southern and eastern Europe.

A study published in Science Advances suggests that the use of betel nut as a drug has older origins than previously thought. Bone remains from two pre-agricultural hunter-gatherers — dated between 25,000 and 16,000 years ago — from Sulawesi (Indonesia) show dental pathology associated with the consumption of these whole nuts. Considered one of the world’s oldest known drugs, when consumed, this nut releases arecoline, the plant’s main neuroactive alkaloid. According to the research, it is possible that the hunters-gatherers’ sole motivation for using it was not merely as a drug, but also for its analgesic and digestive properties.

A Danish team has analysed a small dataset comprising 685 pregnant women and 302 of their daughters at three months of age to assess possible associations between foetal exposure to paracetamol and the infants’ ovarian function. Their study, published in the journal Human Reproduction Open, suggests that girls whose mothers took paracetamol during pregnancy had smaller ovaries and uteri, fewer ovarian follicles and lower levels of reproductive hormones. The authors point out that this is an observational study and therefore cannot assess whether the drug causes reproductive problems or whether these early differences are clinically significant.

Infection with the bacterium Helicobacter pylori is a known risk factor for stomach cancer. Its link to colorectal cancer, however, remains an unconfirmed hypothesis. An international team has reviewed 43 studies on this subject and found that 22 per cent of colorectal cancer cases could potentially be linked to this infection, although when they selected the 14 most reliable studies, the figure fell to 12 per cent. According to the authors, exposure to Helicobacter pylori could be contributing significantly to the number of cases of colon cancer worldwide, but they point out that their study is only exploratory and that more robust research, such as clinical trials, is needed to establish a causal link. The results have been published in eGastroenterology.

A study has analysed structural changes in the female brain during the three main hormonal transitions: puberty, pregnancy and the menopause. To do this, using longitudinal neuroimaging – which records images of the brain over time – the researchers compared women transitioning from one hormonal phase to another with participants currently in those hormonal phases – more than 1,000 women in total. The results, published in Nature Communications, show that the transitions of puberty and pregnancy lead to a reduction in cortical grey matter, whilst women going through the menopause did not show a significant decrease in either cortical grey matter or total brain volume.

Various studies have shown that smokers have a lower risk of developing Parkinson’s disease, but the causes remain unknown. A study has analysed the role played by carbon monoxide — a toxic gas produced by the combustion of tobacco — in this association. To this end, the team conducted a twelve-year follow-up study of more than half a million adults in China. The results show that regular smoking was associated with an increased risk of lung cancer, ischaemic heart disease, stroke and all-cause mortality, but with a lower risk of Parkinson’s disease. Most strikingly, amongst people who had never smoked, higher levels of exhaled carbon monoxide—which the authors measured—were associated with a lower risk of Parkinson’s disease. According to the study, published in JAMA Neurology, these findings demonstrate a possible protective role of carbon monoxide in the disease, rather than smoking itself.

Following the publication of the results of the PISA 2025 report, the question arises as to how to interpret them and explain the possible causes of the decline in reading and maths results, both internationally and in Spain. We have sought the views of experts in education, sociology, inequality, educational technology and pedagogy.

The artificial intelligence (AI) company OpenAI has unveiled GPT-6 Astra, “the world’s smartest and best-aligned model”, according to the company. The new model will use a technique known as ‘opaque recurrence’, which allows it to operate outside the sequential thinking of most reasoning models and which is causing concern amongst AI safety experts due to the possibility that the model’s thought process may be more difficult to monitor.

The peaks of European mountains such as the Pyrenees or the Sierra Nevada may be gaining plant species as the climate warms, but this apparent increase in biodiversity is masking a growing wave of local extinctions. These are the main conclusions of a study published in the journal Science, which includes Spanish participation and analyses nearly a thousand vegetation plots spread across 62 European mountain peaks. The reason is that higher-altitude mountain regions have gained plant species in recent decades as plants from lower altitudes have expanded up the slopes, but this may mask the decline or disappearance of specialised, high-altitude resident species.